Electronic protection devices (also referred to as “fuses” or “circuit breakers”) are designed to protect a conductor (e.g., a wire) against over-current and short-circuit incidents. To prevent over-heating and potential damage to the conductor, an electronic protection device is conventionally configured to trip before a thermal capacity of the conductor is exceeded.
Solid state devices, including solid state power controllers (SSPCs) mimic the behavior of fuses and circuit breakers by monitoring the current passing through the conductor and calculating the amount of power (I2R) dissipated by the conductor over time. The trip time of the solid state devices is inversely proportional to the dissipated power (i.e., the square of current). The trip characteristic of these devices, which determines the trip time, is often referred to as the I2t trip characteristic (where the term “I2t”, or ampere-squared-seconds, is an expression of the energy or heat generated by electrical current) and may be mathematically expressed through the following equation:
                                          ∫                          t              ⁢                                                          ⁢              0                                      t              ⁢                                                          ⁢              1                                ⁢                                                    (                                                      I                    2                                    -                                      I                    Threshold                    2                                                  )                                            I                Rated                2                                      ⁢                                                  ⁢            d            ⁢                                                  ⁢            t                          ≥                  K          1                                    Equation        ⁢                                  ⁢        1            
where I is the load current passing through the conductor, IThreshold is the trip threshold current (or fault current), IRated is the nominal current rating of the conductor, and K1 is a constant. Equation 1 may be restated in a simplified form as∫t0t1I2dt≥K2  Equation 2
where K2 is a constant that accounts for K1, IRated and IThreshold.
When the accumulated value of the integrals of Equations 1 and 2 exceed K1 and K2, respectively, the electronic protection device trips and isolates the fault. This trip characteristic is graphically represented by curve 10 of FIG. 1.
Conventional implementations of the above I2t trip characteristic involve the use of complex circuits, which include multipliers for squaring a current value and integrators for integrating the squared current over time, to achieve a true I2t trip characteristic. However, the use of a multiplier may increase the size, complexity, power consumption, and cost of the electronic protection device and reduce its reliability.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.